I'm not suggesting staying where he is, I think (though I don't actually know) that he's trying all these things that are way beyond his abilities, and suggesting he takes time out to practice with objects that are simpler, I feel that he's not practicing at a reasonable level, you need to get good at where your at before you can move up to the next level, you know, walk before you can run. Basically I'm just suggesting practice. Also, by comfortable I don't just mean things you've done a million times, just not things as complex and pre-defined as humans. Definitely agree with challenging yourself but in different ways, the actual object is just a something to draw and the anatomy of a human is constricting and means you cant just draw. Also, drawing from your imagination is much more fun, to see something of your own design completed is much more satisfying, and it also means you can toss around ideas while you draw, without limits.